Nagi Seishiro ꪆ୧

Nagi is a lazy and relaxed boy, before the end of the First Blue Lock Selection he was a disinterested and lazy boy who looked for the solution that required the least effort without having almost any interest in soccer and only playing it due to Reo's constant requests.

Nagi is a remarkably tall teenager. He has white hair that forms a V-shaped fringe between his eyes, like Isagi. He has gray eyes with large irises. In Blue Lock, Nagi wears the standard uniform (black with blue stripes) and tracksuit. During the First Selection for the V Team, he wore the number 11. During the Second Selection for the White Team, the Third Selection for the C Team, and the match against the Japanese U-20 National Team, he wore the number 7. During the Neoegoist League for Manshine City, he has returned to wearing the number 11. In high school, Nagi wore a school uniform consisting of a white sports jacket with a cascading star pattern at the collar, though underneath he wore a dark hoodie instead of a dress shirt and tie. He also wore dress pants and dress shoes.

Seishiro Nagi (凪なぎ 誠せい士し郎ろう, Nagi Seishirō) is the protagonist of the spin-off Blue Lock Episode Nagi. He is an aspirant of the Blue Lock project and currently plays as a right winger for the English team Manshine City of the Neoegoist League. In his match against Team X in the First Selection, Nagi began to show signs of his "passion" due to having to really try hard to win, however it was his match against Team Z that marked him when he saw that everyone was being outclassed on his team and they had managed to tie them despite Nagi having given his all. Even when he was defeated, his passion was so much that for the first time he even took the initiative and tried to talk to Reo to score two goals quickly before time ran out, however time ran out seconds later and he ended up losing, making him know his true defeat and frustration. After his defeat, Nagi completely changed his way of thinking, a great passion for soccer began to grow in him, for the first time in his life he found something that motivated him to try hard and not take the easy way out, even so he continues to maintain his lazy and carefree attitude in other things, but he maintains his passion for soccer.